Modern sheetmaking equipment, particularly equipment for the manufacture of sheet paper, uses a series of actuators distributed over the sheet being manufactured to adjust the various properties of the sheet such as caliper, moisture content, etc. The actuators control properties over the length of the sheet in the direction the sheet is moving on the equipment (the machine direction (MD)), and also across the width of the sheet in the cross direction (CD). Various sensors are positioned at locations along the sheet under manufacture to scan properties of the sheet and collect data to establish a profile across the sheet with respect to a particular property. This data is processed by a supervisory controller and control information (control actions, setpoints, status, positions) fed back to the appropriate actuators to adjust the properties under their influence toward a desired goal.
Conventional cross direction profile control and machine direction control reside in a hierarchical structure of a supervisory computer and an independent, distributed set of regulatory controllers performing basic actuator regulation in accordance with instructions from the supervisory computer. Profiles and other measured values are sent to the supervisory computer which generates setpoints and sends them to the various regulatory controllers which are responsible for moving and maintaining the associated actuators at the desired supervisory setpoint. The control algorithms to determine the position, movement power level of the actuators is centralized in the supervisory computer.
There is generally some coordination performed by the supervisory computer of the setpoints determined for machine direction control, such as decoupling the weight and moisture MD control. There is also some coordination performed by the supervisory computer for CD control such as coordinating the use of steam and rewet actuators controlling the moisture profile. However, there is little overall coordination of all the CD actuators controlling all the various property profiles such as weight, moisture, and caliper. In general, there is little or no coordination between MD properties and CD properties performed by the supervisory computer.
In conventional sheetmaking equipment, the distribution of the supervisory and regulatory control in a hierarchy allows dedicated computer use for specific purposes. In the past, this arrangement had advantages when slower computers and input/output devices were all that were available. This arrangement also has speed advantages since the regulation of one actuator or a set of actuators is performed independently of other actuators. At the same time, it follows that independent operation at the regulatory level of different sets of actuators does not allow various sets of actuators to be aware of upstream actions with the result that different sets of actuators may work against each other.